When BB6 quizzes haven't been "deployed" - the export is slightly different and the import into Moodle fails.

usually BB6 exports the questions into the file called "res00001.dat" but if the quiz hasn't been deployed then the questions are actually in the file called res00002.dat - the function readdata() in question/format/blackboard_6 should check to see if the questions exist in res00001 and if not use res00002.dat instead.

more info in this forum post:
http://moodle.org/mod/forum/discuss.php?d=155794